The present invention relates to a variable displacement compressor for vehicle air-conditioning.
In a prior art variable displacement compressor shown in FIG. 4, a drive shaft 103 is rotatably supported in a housing 101, which includes a crank chamber 102. The front end (left end in FIG. 4) of the drive shaft 103 projects from the housing 101 and is coupled to an engine (not shown). A lip seal 104 is located between the housing 101 and the drive shaft 103 to prevent leakage of fluid along the surface of the drive shaft 103.
A lug plate 117 is fixed to the drive shaft 103 in the crank chamber 102. The lug plate 117 is coupled to a swash plate 105 via a hinge mechanism 116. The swash plate 105 is supported by the drive shaft 103 to axially slide and incline with respect to the axis L of the drive shaft 103. The hinge mechanism 116 causes the swash plate 105 to integrally rotate with the drive shaft 103. A limit ring 106 is located on the drive shaft 103. When the swash plate 105 abuts against the limit ring 106, the swash plate 105 is at the minimum inclination position.
The housing 101 includes cylinder bores 107, a suction chamber 108, and a discharge chamber 109. A piston 110 is accommodated in each cylinder bore 107. Each piston 110 is coupled to the swash plate 105. A valve plate 111 separates the cylinder bores 107 from the suction chamber 108 and the discharge chamber 109.
When the drive shaft 103 is rotated by a vehicle engine, the swash plate 105 reciprocates the pistons 110. This draws refrigerant gas from the suction chamber 108 to the corresponding cylinder bore 107 via a suction port 111a and a suction valve 111b, which are formed in the valve plate 111. Refrigerant gas in the cylinder bore 107 is compressed to reach a predetermined pressure and is discharged to the discharge chamber 109 via a discharge port 111c and a discharge valve 111d, which are formed in the valve plate 111.
An axial spring 112 is located between the housing 101 and the drive shaft 103. The axial spring urges the drive shaft 103 in the frontward direction (leftward in FIG. 4) and prevents axial chattering of the drive shaft 103.
A bleed passage 113 connects the crank chamber 102 to the suction chamber 108. A pressurizing passage 114 connects the discharge chamber 109 to the crank chamber 102. A displacement control valve 115, which is an electromagnetic valve, adjusts the opening size of the pressurizing passage 114.
The displacement control valve 115 adjusts the flow rate of refrigerant gas from the discharge chamber 109 to the crank chamber 102, which varies the pressure in the crank chamber 102. This varies the inclination of the swash plate 105, the stroke of the pistons 110, and the compressor displacement.
When there is a relatively great cooling demand on a refrigeration circuit that includes the compressor of FIG. 4, for example, when the temperature in a passenger compartment of a vehicle is much higher than a target temperature set in advance, the control valve 115 closes the pressurizing passage 114 and maximizes the compressor displacement.
In this state, when the cooling demand decreases, the control valve 115 quickly and fully opens the closed pressurizing passage 114. Also, when the vehicle is suddenly accelerated while the compressor is operating at the maximum displacement, the control valve 115 quickly and fully opens the pressurizing passage 114 to minimize the displacement to reduce the load applied to the engine.
Accordingly, refrigerant gas in the discharge chamber 109 is quickly supplied to the crank chamber 102, which rapidly increases the pressure in the crank chamber 102 to a high pressure level. Since the amount of refrigerant gas that flows to the suction chamber 108 through the bleed passage 113 is limited, the pressure in the crank chamber 102 quickly increases.
Therefore, the swash plate 105 (as shown by the broken line in FIG. 4) is pressed against the limit ring 106 by a relatively great force when at the minimum inclination position. The swash plate 105 consequently pulls the lug plate 117 in the rearward direction (rightward in FIG. 4) via the hinge mechanism 116. As a result, the drive shaft 103 moves axially against the force of the axial spring 112.
When the drive shaft 103 moves rearward, the pistons 110, which are coupled to the drive shaft 103 via the swash plate 105, also move rearward. Therefore, the top dead center positions of the pistons 110 move toward the valve plate 111, which may cause the pistons 110 to repeatedly collide with the valve plate 111. This generates noise and vibration.
When the drive shaft 103 moves rearward, the axial position of the drive shaft 103 relative to the lip seal 104, which is retained in the housing 101, changes. Normally, a predetermined annular area of the drive shaft 103 contacts the lip seal 104. Foreign particles and sludge adhere to a surface of the drive shaft 103 that is axially adjacent to the predetermined annular area. Therefore, if the axial position of the drive shaft 103 relative to the lip seal 104 changes, sludge enters between the lip seal 104 and the drive shaft 103. This lowers the effectiveness of the lip seal 104 and results in gas leakage from the crank chamber 102.
An objective of the present invention is to provide a variable displacement compressor that prevents the pressure in the crank chamber from increasing to an excessive degree.
To achieve the above objective, the present invention provides a variable displacement compressor compressing gas supplied from an external circuit and returning the gas to the external circuit. The compressor comprises a housing, a cylinder bore formed in the housing, a crank chamber formed in the housing. A suction chamber is formed in the housing such that the suction chamber is connected with the external circuit. Gas is supplied from the external circuit to the suction chamber. A discharge chamber is formed in the housing. A valve plate separates the cylinder bore from the suction chamber and the discharge chamber. A piston is accommodated in the cylinder bore. The piston draws gas from the suction chamber to the cylinder bore via the valve plate. The piston discharges gas, which has been compressed in the cylinder bore, to the discharge chamber via the valve plate. A drive shaft is supported in the housing. A drive plate is coupled to the piston for converting rotation of the drive shaft to reciprocation of the piston. The drive plate is supported on the drive shaft. The drive plate moves between a maximum inclination position and a minimum inclination position in accordance with the pressure in the crank chamber. The inclination of the drive plate determines the piston stroke and the displacement of the compressor. A pressure control mechanism controls the pressure in the crank chamber to change the inclination of the drive plate. A discharge passage passes through the housing and the valve plate to connect the discharge chamber to the external circuit. Gas is sent from the discharge chamber to the external circuit through the discharge passage. A check valve is located on the valve plate to selectively open and close the discharge passage. The check valve is a reed valve. The check valve checks gas flow from the external circuit to the discharge chamber.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.